This competing renewal application combines biochemical, molecular genetic and behavioral analyses to probe the mechanism of action of lysergic acid diethylamide (LSD) and other hallucinogenic drugs. In this revision, the most significant modification is the inclusion of new preliminary results that document feasibility and experimental approach. The experimental plan takes advantage of genetically modified mice and new methods of gene transfer for manipulating signal transduction molecules in behaving animals, allowing us to unite our biochemical and behavioral investigations of hallucinogenic drugs and ask questions never before possible. To accomplish this goal, we have established a drug discrimination assay for hallucinogenic drugs in mice; initial studies suggest that the ergot hallucinogen LSD and the hallucinogenic amphetamines have overlapping but distinct stimulus properties; the mechanism is explored in specific aim 1, including possible agonist-directed trafficking of the intracellular signal. Specific aim 2 utilizes 5-HT2c receptor null mice to test the hypothesis that an absence of the 5-HT2c receptor and its putative antagonism of the 5-HT2A receptor will enhance the cue value of LSD. Preliminary studies in mutant mice support this hypothesis and are bolstered by comparable results using 5-HT2c receptor antagonists in adults. The absence of such pharmacological validation was a major criticism of the previous grant. Our cfos mapping and microinjection experiments have identified the anterior cingulate cortex as an anatomical target for LSD action. We will exploit this finding in Specific Aim 3 by stereotaxically injecting lentiviral vectors encoding proteins that modify intracellular signaling to delineate the signaling pathways that regulate the stimulus properties of hallucinogens. Viral-mediated gene transfer allows the manipulation of signaling pathways in specific brain sites of adult mice, thus avoiding potential developmental or other nonspecific effects in knockout mice. Viral delivery will be linked to genetic manipulation (adult heterozygous Gq mutant mice) to test for synergy between Gq blocking peptide and knockdown of the Gq protein. Explaining the mechanism of action of a powerful hallucinogen such as LSD, which produces profound alterations in cognition, mood, and perception, may lead to a better understanding of why people abuse these drugs and how these processes go awry in mental diseases, such as schizophrenia.